Why is legacy code hell on earth?

New app idea, fatass.app
app where you track everything you eat, if you eat less than your daily protien intake a vineboom sound effect shows up on your phone regardless of device settings with a skull emoji. If you eat too much calories a fat anime girl picture vine boom sound effect. if you dont drink enough water this shows up with vine boom sound effect.

#appidea
#developers
#c++